Lumber mills and other wood processing facilities typically generate wood scraps of various sizes. In plywood processing mills, for example, the wood scraps can be in the form of thin, elongate, veneer-like strips. To be useful in the manufacture of paper, cardboard, and other recyclable materials, wood scraps must be reduced into wood chips having an acceptable size and shape. Mills use screens to separate acceptable wood chips from oversized wood chips. The oversized wood chips are sometimes referred to as overs because they pass over the separating screens.
Ideally, the overs need to be reduced to wood chips that are relatively uniform in size, having gross dimensions of approximately one inch or less. The desirable chip size may vary, depending upon the intended use. Several different types of machines have been tried for reducing overs, such as disc chippers, drum chippers, chip hogs, and the like. These machines often crush or pulverize the overs into unusable bits that are unacceptable for use in making paper, for example.
Mills typically generate a nearly steady flow of overs during wood processing, creating a concomitant need for a system capable of processing overs continuously. The flow of incoming overs may vary greatly, from zero to a large batch, depending upon the mill operations. Most available systems are not capable of adapting to changing volumes without interrupting processing or requiring expensive manual labor when a system becomes jammed or overloaded.
The presence of metal objects in batch wood processing presents an ongoing challenge to facilities where equipment is both expensive and sensitive to damage from metal. The cost and delay of stopping a major piece of equipment to remove metal or repair the damage it caused represents an unacceptable expense for most facilities. Even small metal objects can cause significant damage, especially to grinders and chippers having an array of closely-spaced saw blades. The machinery in use, for example, to reduce overs into small wood chips may be particularly vulnerable to damage from small metal objects.
Thus, there is a need in the art for improvements for the task of safely reducing overs to an acceptable and useful size, efficiently and steadily, during ongoing mill operations.